1. Field of the Invention
The invention relates to a device and a method for molding bistable magnetic alloy wire.
2. Description of the Related Art
Certain ferromagnetic alloy materials, such as Fe—Ni alloy, Fe—Co—V alloy and so on, have different magnetic properties due to different modeling methods. The greater the deformation generated by a material process, the higher the energy required to alter the state of the magnet (i.e. the coercivity will be larger); and conversely, the smaller the degree of deformation, the weaker the energy required to alter the state of the magnet (i.e. the coercivity will be smaller). In a proper technical condition, an alloy wire with uniform components can be formed into a magnetic wire with dual magnetism, namely, a relatively soft core and hard shell.
This kind of alloy wire features a bistable magnetic performance: firstly, a magnetic field is applied outwards along an axis of the alloy wire, so as to make it saturatedly magnetized, after the magnetic field is removed, due to a high coercivity of the shell and low coercivity of the core, the magnetized shell will maintain in a magnetized direction, and the core is magnetized in an opposite direction due to a bias imposed by the remaining magnetism of the shell. Then, as an opposite magnetic field with large intensity is applied, the magnetization direction of the core will be instantly changed into the same state as the shell. Thereafter, as the outside magnetic field is removed, under the action of the remaining magnetism of the shell, the magnetization direction of the core will be changed to its initial state. The bistable alloy wire can be used in many ways, for example, to produce magnetic storage components or pulse generators, and is a key material to make zero power consumption transducer (a magnetic transducer without a power supply).
At present, manufacture of bistable magnetic alloy wires employs a technology disclosed in U.S. Pat. No. 3,820,090; i.e., the alloy wire is firstly processed by heat treatment, and then by cold treatment. Heat treatment refers to a process of continuously heating the alloy wire, then cooling down, and repeating the process several times, so as to vary the eddy current of an inner layer of the alloy wire from that of the core, and to form a shell with relatively large thermal deformation. The cold treatment processing involves mechanical stretching or mechanical twisting. The mechanical stretching is a process where a pair of opposite forces parallel to the alloy wire are applied to a surface of the alloy wire to increase deformation of the shell; the mechanical twisting is a process where a segmented positioning alloy wire is twisted around an axis back and forth, a line with a unit length is twisted for multiple loops (e.g. 10 loops) in a clockwise (or counterclockwise) direction, and then for the same or different loops in an opposite direction. A permanent torque can be maintained or removed, so that an outer circle of the alloy wire generates a relatively large deformation, and the core maintains small deformation via the mechanical stress method.
An object of dual cold treatment processing is to further increase deformation of the shell, to maintain relatively small deformation of the core, and thus forming a magnetic wire with a relatively soft core and a relatively hard shell.
There are two types of cold treatment devices for a bistable magnetic alloy wire:
1) Mechanical stretching device, comprising a feed reel, a feed roller, a receiving roller, a receiving reel, and two pairs of separated wheels. An alloy wire from the feed reel consecutively passes the feed roller, the wheels, the receiving roller, and finally enters the receiving reel. The receiving reel operates via an electromotor, and a rotating speed of an anterior pair of wheels is less than that of a back pair of wheels, and therefore a tensile force is applied to a surface of the alloy wire, which generates much larger permanent deformation of the shell than of the core.
Disadvantages of these conventional stretching devices are: deformation on the surface is relatively small, and the magnetism of the processed alloy wire is not very high.
2) Mechanical twisting device, which can be a common winding machine. Both ends of a segmented alloy wire are fixed on two fixtures of the winding machine, so as to tighten the alloy wire, after that the fixtures are twisted around an axis of the alloy wire for multiple loops (e.g. 10 loops) in a clockwise (or counterclockwise) direction, and then in an opposite direction for the same number of loops, so that there is a relatively significant deformation on the shell of the alloy wire, and the core maintains a relatively small deformation from the mechanical stress method.
Conventional twisting devices need to segment alloy wires for further processing, which has the following disadvantages: 1) continuous production cannot be achieved, and processing efficiency is low; and 2) the degree of twisting and deformation of each part of the alloy wire is different, which leads to non-uniform magnetism of the alloy wire, and affects applications of the alloy wire in a precision apparatus.